This code will disable comments everywhere on your site, and remove all comment-related functionality from the WordPress admin area. It's a nuclear option, but if you want to ensure comments are completely disabled, it should do the trick.

kill-comments.php

<?php

/**
 * Disable support for comments and pingbacks in post types
 */
function suntraxfl_disable_comments_post_types_support(): void {
	$post_types = get_post_types();
	foreach ( $post_types as $post_type ) {
		if ( post_type_supports( $post_type, 'comments' ) ) {
			remove_post_type_support( $post_type, 'comments' );
			remove_post_type_support( $post_type, 'trackbacks' );
		}
	}
}
add_action( 'admin_init', 'suntraxfl_disable_comments_post_types_support' );

/**
 * Close comments on the front-end
 *
 * @return bool
 */
function suntraxfl_disable_comments_status(): bool {
	return false;
}
add_filter( 'comments_open', 'suntraxfl_disable_comments_status', 20, 2 );
add_filter( 'pings_open', 'suntraxfl_disable_comments_status', 20, 2 );

/**
 * Hide existing comments
 *
 * @param array $comments Existing comments.
 * @return array
 */
function suntraxfl_disable_comments_hide_existing_comments( array $comments ): array {
	return array();
}
add_filter( 'comments_array', 'suntraxfl_disable_comments_hide_existing_comments', 10, 2 );

/**
 * Remove comments menu item
 */
function suntraxfl_disable_comments_admin_menu(): void {
	remove_menu_page( 'edit-comments.php' );
}
add_action( 'admin_menu', 'suntraxfl_disable_comments_admin_menu' );

/**
 * Redirect any user trying to access comments page
 */
function suntraxfl_disable_comments_admin_menu_redirect(): void {
	global $pagenow;
	if ( 'edit-comments.php' === $pagenow ) {
		wp_safe_redirect( admin_url() );
		exit;
	}
}
add_action( 'admin_init', 'suntraxfl_disable_comments_admin_menu_redirect' );

/**
 * Remove comments metabox from dashboard
 */
function suntraxfl_disable_comments_dashboard(): void {
	remove_meta_box( 'dashboard_recent_comments', 'dashboard', 'normal' );
}
add_action( 'admin_init', 'suntraxfl_disable_comments_dashboard' );

/**
 * Remove comments links from admin bar
 */
function suntraxfl_disable_comments_admin_bar(): void {
	if ( is_admin_bar_showing() ) {
		remove_action( 'admin_bar_menu', 'wp_admin_bar_comments_menu', 60 );
	}
}
add_action( 'init', 'suntraxfl_disable_comments_admin_bar' );